Recent research in the field of micro-power technology has successfully demonstrated technology with the ability to control micro-scale combustion of liquid hydrocarbon fuels. Potential applications of micro-combustion technology include new generations of batteries, portable chemical reactors, and micro-robots and rovers. For example, see Femandez-Pello, A. Carlos; “Micro-Power Generation Using Combustion: Issues and Approaches,” 29th International Symposium on Combustion, Jul. 21-26, 2002 Sapporo, Japan. Given the ability to store substantial amounts of power in a compact volume, more applications are expected that will impact many fields of technology.
In comparison to current state-of-the-art battery technologies, liquid hydrocarbon has a significantly higher energy density than the highest-capacity battery. For example, a typical Li-Ion battery has an energy density of 0.5 MJ/Kg, while many hydrocarbon fuels can deliver an energy density of 45 MJ/Kg. With its extremely high energy density, liquid hydrocarbon possesses desirable attributes as a power source for portable power generators.
Many approaches have been taken to harvest energy generated by combustion from liquid fuel for conversion into electricity. These approaches include producing pressurized gas to actuate a micro-turbine and generator or heating a thermoelectric generator and producing thermal radiation for conversion by a photovoltaic device. A further approach to power generation is the use of a fuel cell where the combustion heat provides the energy to break down storable gases (such as ammonia) into hydrogen that is subsequently used by the fuel cell to produce electricity.
The energy production capacities of micro-generators have typically fallen into two broad ranges depending on the size of the system. Micro-scale systems (for example, millimeter sizes) have produced power from micro-watts to milli-watts; while meso-scale systems (for example, centimeter sizes) have yielded from tens to hundreds of watts. The manufacturing method and complexity are significantly different between these two types of systems: Micro-scale systems are integrated devices manufactured using silicon processing while meso-scale devices typically involve complex assemblies of miniature components and involve elements that operate at high speeds such as micro-engines.
In reviewing demonstrated power of various systems, it is apparent that no micro-scale system is capable of producing power of around a few watts. A power source producing a few watts of power is of great commercial interest because of it meets the requirement for portable electronic products such as cell phones, laptop computers and gaming devices. Several hybrid systems, however, have demonstrated a near one watt power output by combining micro-combustion with commercial thermoelectric modules.
While research in the field of micro-combustors has made substantial progress, Applicant is unaware of any development to date that has reported net positive power generation. Mostly, the electrical power needed for operating accessory equipment such as pumps, valves and a mass flow controller are excluded from these prior art systems' power calculations. To yield a net positive power, it is necessary to develop an ultra-low power system that includes, in addition to a fuel-efficient micro-combustor, the components necessary to sustain stable combustion, handle fuel transport evaporation, mixing flow control, interface sensors and related electronics. Currently, the efficiency of conversion rates from heat-to-electricity in micro-combustors remains a major issue, but low-power accessory components are also equally lacking. Other challenges in the development of an ultra-low power system include system manufacturability, reliability, and of course the cost of fabrication.
Multiple approaches are necessary to achieve net positive power generation. First, rigorous thermal management is needed to ensure heat generated by combustion is directed into an electrical generator with minimum loss to the environment. Second, ultra-low power fluid and gas handling components are needed. Third, an efficient method for integrating the combustor with accessory components is needed. Lastly, although not related to the net power issue, it is vital that the resulting micro-system can be produced in high volume and at effective cost.